I have to say that 4th May, 2008 was the longest day of my life till now, not just because it never seemed to get over, but also because I actually spent more than 24 hours (28.5, to be precise) in it. Well, the reason, of course, was that I started and ended the day in two different countries (India and Scotland, respectively). However it did make me think on two rather interesting questions – 1. Can one spend a day longer than this? 2. What would be the length of the longest day one can possibly spend being on earth? Obviously, the answer to the first one should be “yes”. It would be too much of a coincidence to unknowingly do something which cannot be outdone as long as you are on earth.
In any case, I did think on the aforementioned questions and after a cup of coffee and some discussions with Eliot Gehrt Setzer, it turned out that the interesting question had a simple answer. The answer, first of all, is 48 hours. Secondly, there are several ways to spend a 48 hours day, an approximate but intuitive way being as follows –
Go to this place called the International Date Line, which, according to wikipedia, “is an imaginary line on the surface of the Earth opposite the Prime Meridian which offsets the date as one travels east or west across it.” Wait there till the start of a new day and start traveling towards west as soon as a fresh day arrives. Remember to keep your speed equal to the speed of the sun (figuratively speaking, of course). This will ensure that its always midnight in the country you are presently in. After just a little less than 24 hours, you will be at a place just a little east of the International Date Line, where it will still be midnight and the date, surprisingly, the same as the one it was when you started. So now you stop and spend your next 24 hours there. At the end you will have spent 48 hours in the same day.
Starting at midnight isn’t really a necessity. The key idea is that you should spend some 24 hours of your 48 hours day without changing the time. This happened to be your first 24 hours in the previous case. It can be the last 24 hours too, or it can be just spread randomly across the day.
Starting at the IDL is a necessity though. That’s because if you don’t start there, then at some point of time you will end up crossing it, resulting in a sudden change of date. Of course, you will have progressed by only one day at the end of your 48 hours in this case too, but you won’t spend all of those 48 hours in the same day.
The above is definitely a good solution as long as you do not mind occasionally traveling to the past. Since the time zones change in a discrete way rather than continuously, even though you are traveling with the sun, so to speak, you will not always remain at midnight (in case you decided to choose the first of the ways described above). You will, depending on the width of the time zones you travel through, keep going back in time by a few hours every now and then. You can however, choose only very narrow time zones to keep such occurrences to the minimum.
Another interesting question arises if you restrict your idea of a “day” to only the time between a sunrise and the next sunset or a date change, whichever happens first. Realize that with this new definition of the day, normal days are less than 24 hours long. They can easily be made equal to 24 hours though, by being at one of the poles during summer. Can we do better? By being just south of the north pole (or north of the south pole) and doing the circle starting at the IDL will do the trick. Being exactly at the pole may lead to some elegant trick, but thinking about the date and time at the pole is scary and I will refrain from getting into it.